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csflag - CARMA shadowing flagging  






CSFLAG is a MIRIAD task which flags correlations where an array of variable sized antennae could geometrically shadow each other. An array of antenna diameters must be given, the number of antenna must be exactly equal that in the dataset. Although UVFLAG can also be used, the current visibility format does not easily allow for variable sized antennae shadowing calculations. Although this program was designed for CARMA, it should work for any heterogenous array.

It is also possible to define a sub-array, and find out if antennas from the remaining antennas are shadowing the antennas in the sub-array. With the caveat of not knowing exactly where the other antennae are pointing, a swept volume algorithm is used for this instead.

Note that this program only SETS flags, never unsets. Multiple runs of csflag with decreasing values of cfraction= will thus NOT have the effect you think it might have. Make a backup of your flags/wflags files if you want to recover. Check with

  uvflag vis= flagval=flag options=noapply
to see how many active flags you have now.  


The input visibility file to be flagged. No default.
Array of diameters (in m) for each antenna. By default all antenna are the same, and equal the antdiam found in the dataset. No default. See also carma= below for a faster approach. Default: not used
Boolean, if set to true, the 23-antenna CARMA array is loaded in the antdiam array. Also it is then assumed the first 6 are OVRO dishes (assumed 10.4m), the next 9 are BIMA (assumed 6.1m), and final 8 for the SZA 3.5m dishes If selected, it will also print out the number of records flagged for O-O, B-B and O-B (labeled O/H/C) for 15-ants and labeled O/H/C/S/10/6 for 23-ants This will also load the Swept Volume descriptors. The default is true.
Special CARMA option to multiply the antdiam array for OVRO and BIMA dishes by. Two or three numbers are expected here, depending if SZA was set or found to be true: fraction for OVRO, that for BIMA, and optionally that for SZA. You normally want this leave this at 1, but can experiment with smaller values to try and keep some partially shadowed data; but check your calibrator(s) how well this is expected to work. Default: 1,1,1
Another cheat, like cfraction, to make the swept volume smaller/bigger by this factor Default: 1
Specify the sub-array (if there is such a thing) for use in the Swept Volume method of flagging. If you specify 0, it will first scan the visibility data to find out which ants are present, and will use these for the sub-array. All other antennas in the antenna position array will then be used in the Swept Volume array. Default: not used.
By default only baselines from the dataset itself are investigated if an antenna of a pair is shadowed. By setting all=true you can allow the other antennae in the array to be taken into account. This is a very conservative algorithm, and is generally not needed in most circumstances. Usually the sarray= keyword is sufficient to compute how the non-subarray antannea are shadowing the subarray in the current dataset. Also known as the Swept Volume method (Eric Leitch) Default: false




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Time: 18:35:38 GMT, July 05, 2011